Vitrifiable flux and bonding composition containing same



VITRIFIABLE FLUX AND BONDING COMPOSITION CONTAINING SAME Filed July 1, 1944 Jajnes JosephKn ox INVENTOR.

; ATTOR/VL'Y Patented Sept. 25, 1945 UNITED STATES VITRIF'IABLE FLUX AND BONDING COMPO- SITION CONTAINING SAME James J. Knox, AveneL'N. J., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application July 1, 1944, Serial No. 543,163

20 Claims.

This invention relates to a new and improved vitrifiabie flux and a new and unique bonding composition containing finely divided particles of said flux and finely divided particles of silver dispersed in a liquid vehicle. The flux, and the bonding composition containing said fiux, of this invention have particular utility in the bonding of metal objects to glass, porcelain or other ceramic objects.

Vitrifiable fluxes have long been used in the ceramic arts as glazes, coatings, decorations, and also, in admixture with finely divided silver particles for the production of bonding compositions.

Bonding compositions of this type may be applied to glass, porcelain or other ceramic articles or structures, the bonding composition fired to fuse the same to the ceramic structure, the fired. coating either electroplated with copper, or bu'rn ished, to produce a surface to which metal objects may be directly soldered to thereby obtain a bond between metal and ceramic. In all such previously known bonding compositions, however, the fired silver-containing coating had to be burnished, or copper-plated, before it would take the solder, i. e., before it would be wet by the molten solder. The step of burnishing, or copper-plating, is costly and time-consuming and often presents difficult problems.

The term ceramic as used throughout the specification and claims is meant to include glass, for example, lime-soda glass, borosilicate glass, metal-borosilicate glass, colored glass, optical glass, and porcelain, for example steatite porcelain, china porcelain and other vitrifiable clays and the like.

Itis an object of this invention to produce a new and improved vitrifiable flux.

It is another object of this invention to produce a new and improved fusible bonding composition comprising, an improved vitrifiable flux and finely divided silver.

It is another object of this invention to produce a new and improved fusible bonding composition comprising an improved vitrifiable flux and ,flnely divided silver, which when fired on a ceramic body will be wetted with solder without first burnishing or copperplating the same.

Other objects of this invention will appear hereinafter.

The new and improved flux of the present invention-comprises between 95% and 50% of bismuth trioxlde (B1203) and between 5% and of a lead-borosilicate composition containing between 30% and 90% PbO, between and 40% SiOz and between 4% and 25% B203.

The new and improved bonding composition of this invention comprises finely divided silver particles and finely divided particles of the above-described flux in a liquid vehicle, the proportion of silver to flux in the composition being between 3:1 and 20:1 and preferably between 4:1 and :1, by weight. This new bo'nding'composition can be applied to a ceramic structure, and firedto a temperature at which the bonding composition 5 fuses to the ceramic structure, to produce a coating on the ceramic structure to which a metal object can be soldered without first burnishing or copper-plating the coating.

As above set forth, the flux must contain be- 10 tween 95% and 50% of bismuth trioxlde and between 5% and 50% of a lead-borosilicate composition. It is to be understood, of course, that beside the bismuth trioxide and the lead-borosilicate, the flux may contain minor percentages of other materials of the type commonly found in vitrifiable fluxes. It is essential, however, that the above-mentioned ingredients be present within the above-defined ranges, and it is also preferred that other materials in the flux be present in total quantity not greater than 15% of the total weight of the flux.

The lead-borosilicate composition, as above stated, must contain between 30% and 90% PbO.

between 5% and 40% S102 and between 4% and 25% B203. This does not, however, preclude the presence of other substances in the lead-borosilicate composition. For example, the lead-borosilicate composition may contain minor percentages of titanium dioxide, cadmium oxide, sodium oxide, barium oxide, magnesium oxide, zinc oxide,

chromium oxide or others. It is essential, however, that the lead oxide, silica and boron oxide be present in the above-defined ranges, and it is also preferred that the PhD, Bio: and B20: make "up at least 80% of the total weight of the leadborosilicate composition. composition may be readily produced in a known "manner, for example, it may be produced by melting red lead, boric acid and flint in the proper o proportions, fritting this =frit in water and drying. The production of other lead-borosilicate compositions is disclosed in U. S. Patent N 0. 2,225,159..

Lead-borosilicate of the above-described composition, in finely divided form, for example, 20 mesh (i. e., 20 meshes per linear inch) or finer is thoroughly mixed with similarly finely divided bismuth trioxide, bismuth subnitrate, or commercial bismuth oxide in such proportions that the bismuth compound, calculated as bismuth trioxide (BizOs) is present in an amount between 95% and of the total weight, and the leadborosilicate is present in an amount between 5% and 50% of the total weight. This mixture is then sintered at a temperature between 650 C. and 750 C. for a period of between 30 minutes and 2 hours. The resulting sintered composition is then ball-milled in water for a period of 1 to 6 hours, and dried. This dried material, which so may have a particle size of about mesh or The lead-borosilicate melt, ball-milling the smaller, constitutes the flux of the present invention.

The bonding composition of this invention may be produced by dispersing in aliquid vehicle between 3 and 20 parts, by weight, of finely divided silver for each part of the above-described finely divided flux. v As will later appear, the silver particles are notnecessarily metallic silver: therefore, the parts by weight of silver are to be taken as parts by weight of metallic silver in the silver particles. The quantity of liquid vehicle in the bonding composition is not critical and may vary between wide limits depending upon whether a paste or liquid composition is desired.

The silver particles should be sufficiently finely divided to pass through a 20-mesh screen (20 meshes per linear inch). They may, however, be considerably finer than 20-mesh size. The silver particles may be in the form of metallic silver, or in the form of silver carbonate or silver oxide, or in any other form which in firing at the temperatures employed will be converted to metallic silver, as is the case with silver carbonate and silver oxide. The terms silver, silver particles" or "finely divided silver as used throughout the specification and claims in connection with the bonding composition before it is fired is meant to include silver in any form which in firing will be converted to metallic silver.

which will not prevent the production of metallic silver during the firing operation. Substances such as turpentine, varnish, turpentine-varnish combinations, pine oil with or without rosin, drying oils, for example, linseed oil, volatile organic vehicles, for example, alcohols, particularly alcohols having between 1 and 8 carbon atoms, ketones, for example, acetone, esters, for example, amyl acetate, ethers, for example, methyl ether of ethylene glycol. Water or water-alcohol mixtures can be used; however, water alone is preferably not used when the object coated with the bonding composition is subject to more or less handling prior to the firing thereof. Under some circumstances, it may be desirable to add a binder to the liquid vehicle. Substances such as polyvinyl alcohol, polyvinyl acetate, nitrocellulose, cellulose acetate and other cellulose derivatives may, for example, be used forthis purpose. When using a binder, it is greatly to be preferred that it be soluble in the liquid vehicle used in the composition.

The bonding composition may be applied to the ceramic object to be coated in any desired manner. For example, it may be applied by spraying, brushing, dipping or by pressing the same through a screen stencil by means of a squeegee. The method of application, and the thickness of coating desired, will determine to a large extent the proportion of liquid vehicle in the composition. The coating should, of course, be thoroughly dried before it is fired. Where the liquid vehicle used is readily volatilized at room temperature (70 F.), the coating may be airdried. Under some circumstances, it may be desirable to .force-dry the coating by means of dry air currents or even by mild baking at temperatures not to exceed about 150 C.

ployed will, of course, depend upon the deformation temperature fthe particular glass being employed in the process. When the bonding composition is fired on a soft glass, a temperature of the order of 1000 F. will be used in the firing operation. When the bondin composition is applied to a heat resisting glass, a temperature of the order of 1100 F.-1150 F. will be used in carrying out the firing operation. The firing period should take place over a period of several hours. Generally, a period of between 1% and 4 hours will be suflicient to produce a good firm bond between the bonding composition and the glass object.

When the ceramic object is porcelain, the firing temperature should be between 1000 F. and

1450 F. depending upon the composition of the porcelain. The firing of porcelain containing a coating of the bonding composition is preferably carried out over a slightly longer period than in the case of glass. Usually, firing for a period from 2 to 4 hours will be sufficient to produce a firm bond between the bonding composition and a porcelain object.

The fired ceramic objects will have a metallized surface which will readily accept solder without previous burnishing or copper-plating. bonding composition of the present invention is considered to be unique in this respect.

The soldering of metal objects to the metallized coatings above described is preferably accomplished with the commonly known soft solder containing approximately equal parts of lead and tin. Such solders may, however, contain small amounts of other metals, for example, silver, as used in known soldering compositions.

The metal to ceramic bond produced in accordance with the present invention has a high tensile strength, which in some cases is limited only by the strength of the ceramic to which the metal is bonded. By bonding glass to metal in accordance with this invention, measured bond strengths as high as 900 pounds per square inch have been obtained.

The accompanying illustrations show several examples of metals bonded to glass in accordance with the principles of the present invention. In the accompanyin illustrations:

Fig. 1 is a sectional view showing an electrical lead wire fastened to a ceramic object,

Fig. 2 is a cross-sectional view of a ceramic tube bonded to a metal cap.

Fig. 3 is a cross-sectional view showing a ceramic bridge bonded to two metal members.

Referring to Fig. l of the drawing, reference W The connecting cap 24 to the metallized bonding composition 22.

In Fig. 3 of the drawing, two metal members 30 are bridged by means of ceramic member 32.

Ceramic member 32 is bonded to the metal mem- Example I Finely divided lead-borosilicate particles (100- mesh size) having the composition:

PbO 74.65 1320; 11.41 s10, 13.94

are thoroughly mixed with similarly finely divided bismuth trioxide (BizOa) in the proportion of 20 parts of lead-borosilicate to 80 parts of bismuthtrioxide. The mixture is sintered at a temperature of 700 C. for about 45 minutes and then allowed to cool. The resulting sintered mass is ball-milled, with a sufficient quantity of water to make a paste, for a period of 3 hours. The resulting pasty mass is then dried at a temperature of 150 C. to form a cake which is readily crumbled to dust or dispersed in a liquid.

The dried flux, produced as above-described, is dispersed, together with finely divided (50- Per cent The resulting sintered mass is ball-milled, with a sufficient quantity of water to make a paste, for a period of 2 hours. The resulting pasty mass is then dried at room temperature to form a cake which is readily crumbled to dust or dispersed in a liquid.

Thedried flux is dispersed together with finely divided (50-mesh size) silver in turpentine in the following proportions:

. Per cent Finely divided silver 65.0 Finely divided fl 15.0 Turpentine 20.0

The resulting liquid bondin composition is applied by brushing on one end of a steatite porcelain tube in the manner shown in Fig. 2 of the drawing. The porcelain tube is fired at a temperature of 1300 C. for a period of 3 hours, and then allowed to cool. over the end of the tube containing the bonding composition and solder applied to the metal cap and the metallized bonding composition as shown mesh size) silver, in a mixture comprising water and 50% ethyl alcohol in the following proportions:

- Per cent Finely divided silver 72.6 Finely divided flux 12.4 Water-ethyl alcohol 15.0

The resulting viscous liquid bonding composition is applied to the surface of (a), a piece of lead-borosilicate glass and (b) to a piece of steatite porcelain. The piece of glass containing bonding composition is fired at a temperature of l000 F.,for 2 hours, and the piece of r porcelain is fired at a temperature of 1250 F. for a period of 3 hours. A piece of copper lead wire is soldered to the fired bonding composition on each object. 0n both the glass and the porce-. lain object the solder readily wetted the metallized bonding composition, and the wire and solder could not be removed from the pieces without fracturing the same.

Example II are thoroughly mixed with a similarly finely divided commercial bismuth oxide in the proportion of 40 parts of lead-borosilicate to parts bismuth oxide. The mixture is sintered at 650 C. for about minutes and then allowed to cool.

in Fig. 2 of the drawing. The solder adheres with such tenacity to the metallized bonding composition that the metal cap cannot be mechanically removed without destroying the end of the porcelain tube.

Throughout the specification and claims, percentages, parts and proportions refer to percent-.

, spirit of the invention. It is, therefore, to be understood that the invention is notto be limited to the above-described detail except as set forth in the appended claims. v

I claim:

1. A vitrifiable flux comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PbO, between 5% and 40% S102 and between 4% and 25% B203.

2. A vitrifiable flux comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PbO, between 5% and 40% SiO2 and between 4% and 25% B201, said bismuth trioxide and said lead-borosilicate composition constituting at least of said flux.

3. A vitrifia'ble flux comprising between 95% and 50% bismuth trioxide'and between 5% and 50% of a iead-borosilicate composition containing between 30% and PbO, between 5% and 40% S102 and between 4% and 25% B203, said PbO, S102 and B20: constituting at least 80% of said lead-borosilicate composition.

4. A vitrifiable flux comprising between and 50% bismuth trioxide and between 5% and 50% of alead-borosilicate composition containing between 30% and 90% PbO, between 5% and 40% SiOz and between 4% and 25% B203, said bismuth A metal cap is positioned.

comprising finely divided silver and flux particles dispersed in a liquid vehicle in a proportion,

by weight, of silver to flux between 3:1'and 20:1 (the weight of silver being the weight of metallic silver in the silver particles), said flux comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate com- ;position containing between 30% and 90% Pb0, 1 between 5% and 40% Si02 and between 4% and 25% B203.

6. A silver-vitrifiable flux bonding composition comprising finely divided silver and flux particles dispersed in a liquid vehicle in a proportion, by weight, of silver to flux between 3:1 and :1 (the weight of silver being the weight of metallic silver in the silver particles), said flux comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PbO,

between 5% and 40% Si02 and between 4% and B203, said bismuth trioxide and said leadborosilicate composition constituting at least 85% of said fiux.

'7. A silver-vitrifiable flux bonding composition comprising finely divided silver and flux particles dispersed in a liquid vehicle in a proportion, by weight, of silver to fiux between 3:1 and 20:1

3 (the weight of silver being the weight of metallic silver in'the silver particles), said flux comprising between 9 5% and 50% bismuth trioxide and between 5% and 50% of alead-borosilicate composition containing between and 90% PbO,

between 5% and 40% Si02 and between 4% and position containing between 30% and 90% PbO,

between 5% and 40% Si02 and between 4% and 25% B203, said bismuth trioxide and said leadborosilicate composition constituting at least 85% of said flux, and said PbO, S102 and B202 constituting at least 80% of said lead-borosilicate composition.

9. A silver-vitrifiable flux bonding composition comprising finely divided silver and flux particles dispersed in a liquid vehicle in a proportion, by weight, of silver to flux between 4:1 and 10:1 (the weight of silver being the weight of metallic silver in the silver particles), said flux comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PbO,

between 5% and 40% SiO2 and between 4% and- 10. A silver-vitrifiable flux bonding composition comprising finely divided silver and flux particles dispersed in a liquid vehicle in a proportion, by weight, of silver to flux between 4:1 and 10:1 (the weight of silver being the weight of metallic silver in the silver particles), said fiux comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PbO,

between 5% and 40% Si02 and between 4% and 25% B203, said bismuth trioxide and said leadborosilicate composition constituting at least 85% of said flux.

11. A silver-vitrifiable flux bonding composition comprising finely divided silver and flux par-'- ticles dispersed in a liquid vehicle in a proportion, by weight, of silver to flux between 4:1 and 10:1 (the weight of silver being the weight of metallic silver in the silver particles, said flux comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PbO,

between 5% and 40% S102 and between 4% and 25% B203, said PbO, S102 and B20: constituting at least of said lead-borosilicate composition.

12. A silver-vitrifiable flux bonding composition comprising finely divided silver and flux particles dispersed in a liquid vehicle in a proportion, by weight, of silver to flux between 4:1 and 10:1 (the ,weight of silver being the weight of metallic silver in the silver particles), said flux comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between30% and 90% PbO, between 5% and 40% S102 and between 4% and 25% B203, said bismuth trioxide and said lead-borosilicate composition constituting at least of said flux, and said PbO, Si02 and B20; constituting at least 80% of said leadborosilicate composition.

13. As a new article of manufacture, a ceramic object containing firmly fused to the surface thereof a bonding composition comprising finely divided metallic silver in a vitreous matrix, the proportion of metallic silver to glass matrix being-between 3:1 and 20:1, said glass matrix comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and PbO, between 5%and 40% S102 and between 4% and 25% B202.

14. As a new article of manufacture, a ceramic object containing firmly fused to the surface thereof a bonding composition comprising finely divided metallic silver in a vitreous matrix, the proportion of metallic silver to glass matrix being between 3:1 and 20:1, said glass matrix comprising between and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PbO, between 5% and 40% Si02 and between 4% and 25% B203, said bismuth trioxide and said leadborosilicate composition constituting at least 85% of said flux.

15. As a new article of manufacture, a ceramic object containing firmly fused to the. surface thereof a bonding composition comprising finely divided metallic silver in a vitreous matrix, the roportion of metallic silver to glass matrix being between 3:1 and 20:1, said glass matrix comprising between 95% and 50% bismuth trioxide' and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PbO, between 5% and 0% S z a tween 4% and 25% B203, said PbO, SiO2 and E203 constituting at least 80% of said leadborosilicate' composition.

16. As a new article of manufacture, a ceramic object containing firmly fused to the surface thereof a bonding composition comprising finely divided metallic silver in a vitreous matrix, the proportion of metallic silver to glass matrix being between 3:1 and 20:1, said glass matrix comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30%- and 90% PbO, between 5% and 40% Si02 and between 4% and 25% B200, said bismuth trioxide and said lead-borosilicate composition constituting at least 85% of said flux, and said PbQ, S102 and B: constituting at least 80% of said leadborosilicate composition.

17. As a new article of manufacture, a ceramic object containing firmly fused to the surface thereof a bonding composition comprising finely divided metallic silver in a vitreous matrix. the proportion of metallic silver to glass matrix being between 4:1 and 10:1, said glass-matrix com prising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PhD, between 5% and 40% SiO2 and between 4% and B203.

18. As a new articl of manufacture, a ceramic object containing flrmly fused to the surface thereof a bonding composition comprising finely divided metallic silver in a vitreous matrix. the

. proportion of metallic silver to glass matrix being between 4:1 and 10:1, said glass matrix comprising between 9.5% and 50% bismuth trioxide and between -5%' and 50% of a lead-borosillcate composition containing between and 90% PhD, between 5% and S10: and between 4% and 25% 3203, said bismuth trioxide and said lead-borosilicate composition constituting at least 85% of said flux. 19. As a new article of manufacture, a ceramic object containing firmly fused to the surface thereof a bonding composition comprising finely divided metallic silver in a vitreous matrix, the proportion of metallic silver to glass matrix being between 4:1 and 10:1, said glass matrix comprising between 95% and bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PbO, between 5% and 40% S102 and between 4% and 25% 1320:, said Pbo, SiOz and B203 constituting at least of said lead-borosilicate compositions.

20. As a new article of manufacture, a ceramic object containing firmly fused to the surface thereof a bonding composition comprising finely divided metallic silver in a vitreous matrix, the proportion of metallic silver to glass matrix being between 4:1 and 10:1, said glass matrix comprising between 95% and 50% bismuth trioxide and between 5% and 50% of a lead-borosilicate composition containing between 30% and 90% PbO, between 5% and 40% SiOz and between 4% and 25% B203, said bismuth trioxide and said lead-borosilicate composition constituting at least of said flux, and said PbO, SiOz and m0: constituting at least 80% of said lead-borosilicate composition.

JAMES J. KNOX. 

